A dual clutch transmission known from practice, is designed as reduction gearing in order to obtain different transmission ratios for forward travel and for backward travel, having a central transmission shaft, a hollow transmission shaft disposed concentrically hereto, a layshaft, and having two powershift elements. Both powershift elements have an operative connection with the drive unit at the input end. One of the two powershift elements is connected to the central transmission shaft at the output end, while the other of the two powershift elements is connected to the hollow transmission shaft at the output end. In order to demonstrate a transmission ratio via gear stages that can be engaged with and disengaged from the power flow via shift devices, the central transmission shaft and the hollow transmission shaft can be connected to the layshaft. In addition, multiple shift devices are each associated with two gear stages.
A dual clutch transmission having a dual clutch, the input end of which can be driven by a drive shaft of an engine, and the output end of which shares a drive connection with one of two gearbox input shafts respectively, disposed coaxially to one another, is known from document DE 10 2005 005 163 A1 . The dual clutch transmission is formed having one intermediate shaft or exactly one layshaft, and features fixed or idler gears attached to or rotatably mounted on shafts, and the shift sets associated with the idler gears. The idler gears can be connected in a rotatably fixed manner via the shift sets in order to realize transmission ratios or transmission steps with each respective shaft. The shift sets are each associated with two gears that do not directly follow one another.
In the case of the two above-described dual clutch transmissions however, only seven transmission ratios are obtainable for forward travel, which is why engines that can be coupled with the dual clutch transmissions, in particular internal combustion engines, cannot be operated in their optimum operating range to the desired extent for a large part of the engines' operating range, especially in terms of available tractive force and low fuel consumption.
DE 10 2007 049 271 A1 describes a dual clutch transmission having at least two layshafts in order to be able to obtain multiple transmission ratios for forward and backward travel.
Due to the design of the dual clutch transmission with two layshafts, this transmission features a greater radial space requirement as compared with dual clutch transmissions having a single layshaft, which is not available to the degree needed in various vehicle systems.